Ask the Experts Metals

How can we minimize infiltration of oxygen into open-ended continuous furnaces?

Tom Philips Sr. Principal Applications Engineer

Oxygen from air can diffuse or infiltrate your furnace from the front and exit ends, causing problems such as oxidation, decarburization, under-sintering or inadequate braze quality. Here are some methods to reduce oxygen infiltration:

Use adequate total atmosphere flow to have a slightly positive pressure inside the furnace. Typically, a flow of about 70 to 100 scfh per inch of belt width is enough for door openings less than 3 inches.

Install a flame curtain at the front end, preferably attached to the bottom of the door, with the flames shooting down onto the parts—ensuring complete coverage of the front end opening.

Install a good fiber type curtain with an additional nitrogen spray curtain at the exit end.

Ensure the exhaust stacks are separated from the furnace and don’t cause differential suction on the furnace’s atmosphere.

For more information or an atmosphere audit by Air Products’ experienced engineers, call 800-654-4567.

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